1. Field of the Invention
The present invention relates to a protective device for a controlling system of a sewage pump, and more particularly to a protective device that controls pump operation and has a protective circuit protecting a start capacitor in the controlling system to avoid the start capacitor from burnout when an overload is occurred by actuating power source (ON status) or when a transient voltage is occurred by malfunction of a controlling circuit.
2. Description of Related Art
A conventional sewage pump system in accordance with the prior art as shown in FIGS. 1 and 2 has an operational controlling circuit system 2 for controlling the operation of a sewage pump 1. The operational controlling circuit system 2 has a start capacitor 21 connected with a run capacitor 22 in parallel connection and a centrifugal switch 3 in series connection and further connected with an actuating coil 11 and an operating coil 12 to perform a combined circuit. In the operational controlling circuit system 2, the actuating coil 11 and the operating coil 12 drive the sewage pump 1 to function when the electrical power is supplied. The centrifugal switch 3 mounted on a shaft 4 of the sewage pump 1 is changed from a normal closed (N.C.) status to a normal open (N.O.) status because the centrifugal force caused by the rotation of the shaft 4 so that the start capacitor 21 is interrupted by discharging movement and stops immediately to protect itself from burnout during long-term operation period. However, the centrifugal switch 3 is usually malfunctioned and thus kept the normal closed (N.C.) status because the carbon accumulation or oxidation caused by sparkles at contacts when a large current is occurred. Therefore, disengagement movement of the centrifugal switch 3 can not be completed and the start capacitor 21 is kept to contact with the power source and to discharge electricity until burnout. Moreover, the actuating coil 11 and the operating coil 12 of the sewage pump are consequently burnt.
According to above description, the conventional sewage pump system still has some drawbacks in use.